ABSTRACT
Then circadian rhythms can persist through the complete anatomical dissolution and reconstruction of insect metamorphosis,c and also through long hibernation in mammals.d It may be possible to localise some biological clocks in particular organs, 'conductors of the physiological orchestra' as it were, for Harker (2) has shown that transplanting the sub-oesophageal ganglion into a headless cockroach induces circadian rhythms of donor amplitude in the previously arhythmic host.e
Among circadian rhythms in mammals there is one of nucleic acid synthesis, so fundamental for all cell-division, growth and repair. A minimum of desoxyribonucleic acid (DNA) synthesis in the liver of the mouse occurs at 04.00 hr but the minimum of ribonucleic acid (RNA) synthesis is at 16.00 hr, parallelling a cycle of activity of the adrenal glands. f Their largest corticosterone production occurs at 18.00 hr.g In man there is a marked circadian rise and fall in the urinary excretion of 17-0H corticosteroids, going along with potassium excretion and body temperature.h This last seems to be adrenal-controlled, like the day and night rhythm of oxygen-consumption, the fluctuation of liver glycogen and phospholipids, and the numbers of leucocytes in the blood. i Again, it is not generally known that the composition of
a Cf. the symposium proceedings edited by Aschoff (I). b Cf. Halberg (I), and especially Hellbriigge (I). C Harker (I), p. ZO. d St Girons (I); over months spontaneous arousals and activity in the garden dormouse (Eliomys
quercinus) invariably occurred between about 17.00 and 04.00 hr. e Cf. also Harker (3), pp. Izff. f Halberg (z); Halberg et ale (I). g Halberg (I). h Halberg (z); Lobban (I). i Roberts (I).
